The present invention relates to a process for regulating the hardening speed of a self-hardening mold for casting of metals. More particularly, the invention pertains to a process for regulating the hardening speed of a self-hardening mold which comprises adding a hardening speed regulating agent when a mold is formed with molding sand prepared by adding a polyvinyl alcohol solution as a binder and a boron compound as a curing agent to refractory particles and then kneading the mixture. Thus, the bench life of the molding sand can be freely regulated by varying the amount of the hardening speed regulating agent added.
When a complex shape mold is desired to be produced with a self-hardening molding sand (a reasonable bench life is required), or when the production of a mold requires a long period of time for other reasons, it is necessary that the hardening speed of molding sand is slow. In other words, a bench life corresponding to the time for the production of a mold is required for molding sand. Generally speaking, it is desirable that the hardening speed of molding sand can be freely regulated.